1. Field of the Invention
This invention relates, in general, to increasing legume crop production by coating legume seeds with a protective and nutritive composition. More specifically, this invention relates to compositions and methods for a seed coating for legume seeds which protect seeds after planting and stimulate plant growth after emergence of the seedlings.
2. Related Art
Seed coatings have been used as means for protecting and enhancing the environment next to the natural seed coat, to control seed germination and/or improve seedling survival and growth rate. Toward these ends, coatings have been used as carriers for a variety of components: agrochemicals, Rhizobium bacteria, nutrients, beneficial elements, and plant growth regulators. Such components can be effective in improving seed germination and seedling survival and growth in the face of diseases, insects, low soil pH, and poor soil fertility. By including these components in seed coatings or pellets, the components are placed at the interface between seed and soil. This close proximity to the interface between seed and soil maximizes the effect of the components and reduces waste and environmental impact compared to the method of broadcasting such components over a field containing uncoated seeds.
Several seed coatings have been described in the patent literature that are intended for protective and/or nutritive purposes. For example, Schreiber (U.S. Pat. No. 3,698,133, issued Oct. 17, 1972) discloses the use of a multiple-layer coating, including an inner, porous, water-permeable coating and an outer polymer layer having a controlled permeability to water. The Schreiber coating is intended to control moisture permeation and delay germination until climatic conditions are satisfactory for continued crop growth. Watts (U.S. Pat. No. 3,947,996, issued Apr. 6, 1976) controls germination by coating seeds with a film-forming composition comprising a water-insoluble polymer and polyvinyl alcohol having an oxygen transmission high enough to maintain viability of the seed. Dannelly (U.S. Pat. No. 4,249,343, issued Feb. 10, 1981) discloses a temporary, disintegrating microgel coating for protecting seeds from mechanical and environmental damage and for carrying fertilizers, herbicides, or pesticides.
In other literature, molybdenum is shown to be a micronutrient for legumes. See, for example, Gupta and MacKay ("Crop Response To Applied Molybdenum and Copper on Podzol Soils", Can. J. Soil Sci., Vol. 48, 235-242 (1968)). Gupta and MacKay reports increases in yields of cauliflower, spinach, barley, timothy and alfalfa after application of Mo and Cu to the soils.
In acidic soils, lime coatings for seeds have been shown to be beneficial to seedling performance. The presence of the lime coating is believed to improve nodulation in soils with pH ranging from about 5.0-5.6. Kunelius and Gupta ("Effects of Seed Inoculation Methods with Peat-Based Rhizobium Meliloti On Alfalfa", Can. J. Plant Sci. 55: 555-563) discusses the performance of alfalfa seed inoculated with Rhizobium meliloti (with and without molybdenum-treating), compared to lime-coated alfalfa seed inoculated with Rhizobium meliloti (with and without molybdenum-treating). Kunelius and Gupta show superior results from the seeds with a lime coating, compared to those without the lime coating. Kunelius and Gupta report that treating with molybdenum did not always increase the alfalfa dry matter yields, the nitrogen content of the alfalfa tissue, or the nodulation of the alfalfa, compared with the results of corresponding seed treatments without added molybdenum. Thus, Kunelius and Gupta conclude that lime coating may be advantageous to vigorous alfalfa stands when broadcasting of limestone onto acidic soils is not practical or desirable.
Gypsum has been suggested as a seed coating. See, for example, McGraw and Bailey, "Efficacy Of Seed Coating To Improve Seedling Survival", a published industry report. In this article, gypsum is listed along with "clays, lime . . . phosphate rock, organic materials, etc.," as a possible seed coating.
Examples of other nutrients and additives for improving plant growth and/or crop production are described in several U.S. patents. Compositions for broadcasting and mixing with soils are described, as well as in vitro culture media. Coke (U.S. Pat. No. 5,534,434, issued Jul. 9, 1996), Yamashita (U.S. Pat. No. 5,549,729, issued Aug. 27, 1996), and College, et al. (U.S. Pat. No. 5,628,811, issued May 13, 1997) are examples of such nutrients and additives.
Coke discloses a basal nutrient medium for in vitro cultures of loblolly pines. The medium includes nitrate, ammonium, potassium, phosphorate, calcium, magnesium, sulfate, chlorine, sodium, borate, manganese, iron, zinc, copper, iodine, molybdenum oxide, cobalt, thiamine and EDTA. Coke discloses use of this medium, comprising many ingredients, for the purposes of asexual propagation, rejuvenation, virus elimination, and genetic transformation.
Yamashita discloses a composition for stimulating growth of plants comprising a long list of preferred ingredients: a carbon skeleton/energy component (typically a sugar or mixture of sugars such as molasses); a macro-nutrient component providing nitrogen, phosphorus, potassium and calcium and preferably also magnesium and sulfur; a micro-nutrient component providing zinc, iron and manganese, and preferably also copper, boron, molybdenum and cobalt; and preferably a vitamin/cofactor component, an enhancement component, and a buffer. Yamashita teaches that the most important nutrients are nitrogen, phosphorus, potassium and calcium, zinc, iron and manganese. Yamashita lists thiamine, riboflavin, nicotinic acid, pyridoxine, folic acid, biotin, pantothenic acid, cyanocobalamin, phosphatidylcholine, inositol, and para-minabenzoic acid as vitamin/cofactors. Yamashita lists as enhancement components such materials as complexing agents, gums, and growth regulators, including seaweed extract, citric acid, Katy-J complexing agent, and Xanthan gum. Yamashita discloses that the media may be applied in the form of an aqueous solution, sprayed at intervals at different stages of the plant growth, or in a form suitable for coating seeds or pollen.
College, et al. discloses a plant-growth enhancement method intended for ameliorating acid soils. In the College method, 0.05 to 20 percent by weight of flue gas desulfurization by-product is mixed into the soil. The flue gas desulfurization by-product consisted of 80-99 wt-% of gypsum and 1-20 wt-% of magnesium hydroxide.
Still, there is a need for improved compositions and methods of protecting and enhancing legume seeds and seedling survival and growth, in order to increase plant vigor and crop production. These is a need for economical and convenient compositions and methods for such seed treatments that can reliably improve seedling performance.